Medium controller with slot-mounted sensors

ABSTRACT

When a medium is stored or removed manually, all slots must be checked to find any change in medium information, and as a result, updating medium storage information takes a long time. A medium controller, having a plurality of media and a medium transfer unit to take a medium in and out of storage and move the medium for reading or writing information, includes slots in which media are stored, sensors each mounted in a slot for detecting whether there is a medium in the slot; a sensor manager for holding a log of the status transitions of the sensors in a period when media are likely to be stored or removed manually and deciding the status transitions; and a part for reading information. Only when it is decided from a decision result of the sensor manager that the medium has been replaced, the media controller causes the part for reading medium information to read medium information in order to update the medium storage information.

This is a continuation of application Ser. No. 09/669,685 filed Sep. 26,2000, now U.S. Pat. No. 6,515,946.

BACKGROUND OF THE INVENTION

The present invention relates to a medium controller for medium-exchangetype memory units that is used as peripheral equipment of a computer(for example, an autoloader in a library of magnetic tape units oroptical disk units).

The events, such as opening or closing of the entry/exit door, resettingor stopping power supply for the medium controller, are hereafterreferred to as medium entry/exit-enable actions. When power supply isstopped or a reset button is pressed, it becomes possible to open orclose the door of, the medium storage and, after that, a medium may betaken out or put into storage. This is the reason why those events aretreated as the medium entry/exit-enable actions. Upon recognizing any ofsuch events, the medium controller has medium storage information withthe contents before this event automatically updated or the system siteoperator issues a command to have the information updated.

Conventionally, when medium storage information is to be updatedautomatically or by the operator issuing a command, the prior-art mediumcontroller is unable to obtain medium entry/exit information becausethere is no sensor to recognize a medium in the medium storage area. Asa solution, generally, the medium transfer unit (accessor) is equippedwith a sensor or a bar-code reader to read a bar code on the medium andthe medium transfer unit is made to access all the medium storage places(hereafter referred to as slots) where media are stored, and each timethe sensor or the bar-code reader, provided for (accompanying) theaccessor, recognizes a medium, the medium storage information isupdated. In the prior-art medium transfer unit, each time some medium isreplaced manually, the medium transfer unit accesses all medium storageplaces as mentioned above, taking a long time. Therefore, there is along waiting time before the medium controller can be accessed from thesystem.

The conventional medium controller cannot grasp the medium storagestatus unless the medium transfer unit (accessor) sequentially checksall the slots; therefore, there are the following two problems.

The first problem is that, in a medium controller with a very largenumber of media in storage, the accessor checks every slot to see whatmedium is stored. This requires a long time for updating medium storageinformation. For this reason, in many cases, medium storage informationis updated only when the operator desires. Consequently, when a mediumis taken out or put into storage especially by manual operation, if theoperator does not update medium storage information, it follows that themedium storage information does not match the actual storage status.

The second problem is that, in a medium controller with fewer media instorage, medium storage information is updated automatically in manycases when the condition that media are exchanged occurs, with theresult that each time a medium comes in or out, the medium controller iskept waiting while the medium transfer unit is accessing all the slotsand cannot perform other processing.

SUMMARY OF THE INVENTION

It is an object of the present invention to greatly reduce time forupdating medium storage information when a medium entry/exit-enableaction occurs during the backup operation of a computer system,particularly in the operation of the, automatic (unmanned) mediumcontroller. This significant time reduction contributes to a substantialsolution of the problem of waiting time before the medium controller canbe accessed. In addition, because it takes a long time to update themedium storage information in the medium controller with a large numberof media in storage, the medium storage information is not necessarilyupdated each time a medium entry/exit-enable action occurs but themedium information is updated only when the operator thinks itnecessary. Therefore, it is another object of the present invention tosolve the problem of the discrepancy between medium storage informationand the actual storage status. This is accomplished by theabove-mentioned significant reduction in time for updating the mediuminformation because this time saving makes it possible to automaticallyupdate the medium storage information when a medium entry/exit-enableaction occurs.

According to a first aspect of the present invention, there is provideda medium controller storing a plurality of media, having a mediumtransfer unit to take a medium in and out of a storage place to read orwrite information on the medium and to transfer the medium to a placewhere reading and writing information is possible, and managinginformation about media in storage. This medium controller comprisesslots for storing media; sensors, each mounted in each of the slots, fordetecting whether or not there is a medium in the slot; a sensor managerfor holding a log of status of the sensors in a period when media arelikely to be taken in or out manually and deciding changes in the statusof the sensors; and a medium information reader for reading mediuminformation, which identifies a medium, from the medium, wherein when itis decided from a decision result by the sensor manager that the mediumhas been replaced, medium information is read by the medium informationreader to thereby update medium storage information, or when it isdecided that the medium has not been replaced, the medium storageinformation is not updated.

According to a second aspect of the present invention, a mediumcontroller further comprises a door open detector for detecting that thedoor is open at the medium storage place of the medium controller; adoor closed detector for detecting that the door is closed; a firstmemory for storing medium management information showing what media arestored in which slots; and a second memory for storing medium managementinformation showing what media are stored in which slots at the momentwhen the door close detector detects that the above-mentioned entry/exitdoor is closed, wherein the medium storage information is updated bywriting the medium information, which was read in by the mediuminformation reader, in the first and second memories.

According to a third aspect of the present invention, there is provideda medium controller, wherein the sensor manager comprises a sensorstatus holder for storing the current sensor status of the respectiveslots; a log tracer for holding a log of the sensor status of therespective slots when it is found from contents of the sensor statusholder that the entry/exit door is opened; and a log, trace determinerfor checking status changes in sensors from contents of the log tracer,wherein supposing that a sensor status that a medium exists isdesignated as ON and a sensor status that a medium does not exist isdesignated as OFF, when a decision result of the sensor status decisionunit is OFF→ON or ON→ON, the medium information is read in by the mediuminformation reader and when a decision result is ON→OFF, the mediuminformation is erased and when a decision result is OFF→ON→OFF or thatthe sensor status remains unchanged, the medium information is not readin by the medium information reader.

According to a fourth aspect of the present invention, there is providedanother medium controller storing a plurality of media therein, having amedium transfer unit to take a medium in and out of a storage place toread or write information on the medium and to transfer the medium to aplace where reading and writing is possible, and managing informationabout media in storage. This medium controller comprises slots forstoring media; magazines each including a plurality of the slots;sensors, each mounted in each of the magazines, for detecting whether ornot a medium has been removed from or stored in a slot; a sensor managerfor deciding detection results of sensors in a period when media arelikely to be taken out or stored manually; and a medium informationreader for reading medium information, which identifies a medium, fromthe medium, wherein when it is decided from a decision result by thesensor manager that the medium has been replaced, medium information isread by the medium information reader to thereby update the mediumstorage information, or when it is decided that the medium has not beenreplaced, the medium storage information is not updated.

According to a fifth aspect of the present invention, yet another mediumcontroller further comprises a door open detector for detecting that thedoor is open at the medium storage place of the medium controller; adoor closed detector for detecting that the door is closed; a firstmemory for storing medium management information showing what media arestored in which slots; and a second memory for storing medium managementinformation after log tracing showing what media are stored in whichslots at the moment when the door open detector detects that theabove-mentioned entry/exit door is open, wherein the medium storageinformation is updated by writing the medium information, which was readin by the medium information reader, in the first and second memories.

According to a sixth aspect of the present invention, there is provideda control method for use in a medium controller storing a plurality ofmedia therein, having a medium transfer unit to take a medium in and outof a storage place to read or write information on the medium and totransfer the medium to a place where reading and writing is possible,and managing information about media in storage. This method comprisesthe steps of skipping an updating of medium storing information when astatus of a sensor remains unchanged in a period when media are likelyto be removed and stored manually, said sensor being mounted in eachslot where a medium is stored and detecting whether or not there is amedium in the slot; and updating the medium storing information byreading medium information from the medium via medium informationreading means when a change is found in the status of the sensor from asensor status log and it is decided from contents of said log that themedium has been replaced.

According to a seventh aspect of the present invention, there isprovided another control method for use in a medium controller storing aplurality of media therein, having a medium transfer unit to take amedium in and out of a storage place to read and write information onthe medium and to transfer the medium to a place where reading andwriting information is possible, and managing information about media instorage. This method comprises the steps of skipping an updating ofmedium storing information when a sensor does not detect a medium isremoved from or stored in a magazine in a period when media are likelyto be stored into and removed from storage, said sensor being installedin the magazine having a plurality of slots each storing a mediumtherein and detecting the removal or storing of the medium; and updatingmedium storing information by reading medium information from the mediumin all slots in the magazine via medium information reading means whensaid sensor detects the storing or removal of the medium and it isdecided from detected contents that the medium has been replaced.

When a medium entry/exit-enable action occurred, the medium controlleraccording to the present invention confirms the spot in the mediumstorage where the sensor status has changed from that before theentry/exit-enable action. If there has not been any change in the statusof the sensor, the medium storage information is regarded as unchangedafter the entry/exit-enable action took place and the information is notupdated.

On the other hand, if a change is found in the status of the sensor, themedium controller confirms changes in the sensor status of therespective slots, and updates medium storage information of only thoseslots where the sensor status has changed, and uses this updatedinformation as information after a medium went out and came in.

More specifically, the medium storage information is updated accordingto the contents of the status changes of sensors. When a medium is inthe slot, let the sensor be ON and when there is no medium in the slot,let the sensor be OFF. For example, suppose that the medium controllermay be able to recognize as follows. When the sensor switches from ON toOFF, the medium has been removed from the slot. When the sensor switchesfrom OFF to ON, a medium has been put in the slot. When the sensorswitches from ON to OFF to ON, the medium has been replaced and finallyput. When the sensor switches from OFF to ON to OFF, a medium has beentemporarily put in the slot and finally removed. If the mediumcontroller can manage medium storage information as mentioned above,when the sensor switches from ON to OFF (the medium has been removedfrom the slot), the medium controller may erase medium storageinformation in the slot. When the sensor switches from OFF to ON to OFF(the medium has been eventually removed), because the medium storageinformation remains unchanged between before and after removal and entryof a medium, the medium controller may not update the medium storageinformation. When the sensor switches from OFF to ON (a medium has beenput in the slot) and when the sensor switches from ON to OFF to ON (themedium has been replaced), the medium controller may check the mediumstorage status for any change with a sensor or a bar-code readerattached to the medium transfer unit, in other words, may read mediuminformation by which to determine a medium that replaced the previous(hereafter referred to as medium information), and may enter mediuminformation after the change in medium storage information. By thisprocedure, medium storage information can be updated accurately with aminimum of action.

If the medium controller automatically updates medium storageinformation as described above, processing time can be reduced markedly.Also with a medium controller managing a very large number of media instorage, even if medium storage information is updated when a mediumentry/exit-enable action occurs, a waiting time in which the mediumcontroller cannot be accessed from the system can be shortenedsubstantially. For this reason, it is possible to make a setting suchthat updating of medium storage information by managing sensor status isexecuted automatically without relying on the operator.

Because the provision of sensors for individual slots costs a large sumof money, it is possible to install sensors at the rate of one sensorfor each group of a certain number of slots (e.g., one for eachmagazine). This method of allocation can be implemented as follows. Forexample, in a case where a sensor is installed for each magazines, themedium controller checks the status of the sensor on each magazine, andthen checks the medium storage status at all slots of the magazine,where a sensor status changed, with a sensor or a bar-code readerattached to the medium transfer unit, and subsequently updates mediumstorage information.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asother features and advantages thereof, will be best understood byreference to the detailed description which follows, read in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a flowchart of a first embodiment of the present invention;

FIG. 2 is a flowchart of a second embodiment of the present invention;

FIG. 3 is a conceptual diagram showing the structure of the firstembodiment of the present invention;

FIG. 4 is a conceptual diagram showing the structure of the secondembodiment of the present invention;

FIG. 5 is a block diagram showing the first embodiment of the presentinvention;

FIG. 6 is a medium storage information table of the present invention;and

FIG. 7 is a sensor status log table of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The configuration of a first embodiment of the present invention will bedescribed with reference to FIG. 5. The medium controller according tothe present invention stores many media therein and is provided with amedium transfer unit to move a medium from the storage place to aposition where the medium can be taken out or put into storage or datacan be read and written on the medium. The medium controller includes adoor open detecting means 19 for detecting that the entry/exit door isopen; a door closed detector 21 for detecting that the entry/exit dooris closed; sensors 2, each mounted in a slot, for deciding whether ornot there is a medium in the slot; a medium storage information memory11 for storing medium management information showing what medium isstored in each slot; a temporary memory 12 for receiving and temporarilystoring medium management information at the moment when the door opendetecting means 19 detects that the entry/exit door is open; sensormanaging means 14 for monitoring the output of the sensors 2 to find achange in the status of the sensors 2; medium information reading means13 for reading medium information from the medium to be identified, anda medium information controller 18 which causes the medium informationreading means 13 to read medium information when it is required from adecision by the sensor managing means 14 to update the mediuminformation and which requires the temporary memory 12 to update themedium storage information based on the medium information, and alsorequires the medium storage information memory 11 to update its contentsstored.

As an example of medium information, FIG. 6 shows medium storageinformation organized as a media storage information table in which theslot locations are associated with stored, different pieces ofinformation used to determine media (hereafter referred to as mediuminformation). The sensor managing means 14 includes a sensor statusholder 15 for storing the current status (ON when there is a medium; OFFwhen there is no medium) of the sensor 2 of each slot; a log tracer 16for holding a log of the sensor status of each slot after the door opendetector detects that the entry/exit door is opened; and a log tracedeterminer 17 for detecting status that the entry/exit door is closedchanges in the sensors from contents of the log tracer 16.

FIG. 7 is a table showing the contents of the log tracer 16, that is, anexample of a log of the sensor status. When the entry/exit door wasopened, the status of the sensors were written in the spaces under thecolumn title of the Sensor Status Log 1, and subsequently, every timethe status of a sensor changed, the status of the sensors were writtenin the spaces at the corresponding slots of the columns of the SensorStatus Log 2, 3 and so on. For example, at the slot 3, the status of thesensor was initially ON, and switched to OFF and finally ON the momentthe door closed detecting means 21 detected that the door was closed.This sequence corresponds to a case where initially a medium was stored,and then the operator opened and closed the door, during which themedium was replaced by another medium. Of course, the result is the samewhen the same medium was dismounted and put back in the same place. Evenif this is the case, it is safer if the medium is regarded as replaced.

The log trace determiner 17 checks which of the patterns shown below thestatus transition of each slot belongs by referring to the table showingthe log of sensor status transitions. The status transitions are:{circle around (1)} OFF→ON (e.g., slot position 2 in FIG. 7); {circlearound (2)} ON→OFF→ON (e.g., slot position 3); {circle around (3)}ON→OFF (e.g., slot position 1); {circle around (4)} OFF→ON→OFF (e.g.,slot position 4); {circle around (5)} the case where the statustransition of a sensor does not occur. In other words, the sate of asensor continues to be OFF and does not switch to ON (e.g., slotposition 6) or the sensor status continues to be ON and does not switchto OFF (e.g., slot position 7). For example, the case of slot 5corresponds to a case where a medium was replaced with another medium,which was further replaced with a third medium, but in this case, toknow the final status, knowing that the third medium is in the slot 5 isenough and it should be decided that the transition in this case is thesame as the transition of OFF→ON in the transition {circle around (1)}.In the transitions {circle around (4)} and {circle around (5)}, therewas no medium either at the beginning or the end, and there being nodifference in subsequent treatment of these cases, these cases may becategorized as the same pattern of status transition. In the cases{circle around (1)}, {circle around (3)}, {circle around (4)} and{circle around (5)}, the transition pattern can be known from theinitial and final sensor status. Only in the case {circle around (2)},the intermediate status is checked, and if it is found to be OFF, adecision may be made that this status transition {circle around (2)}corresponds to the pattern {circle around (3)}, or if the intermediatestatus is found to be not OFF, the status transition {circle around (2)}corresponds to the pattern {circle around (5)}.

Description will now be made of the operation of the first embodimentwith reference to FIG. 1. FIG. 1 is a flowchart of the updating processof medium storage information when sensors are mounted at all andindividual slots. The sensors to be mounted are any of those which candecide whether or not there is a medium in the slot (such as an opticalsensor, a contact sensor, or a weight sensor). FIG. 3 shows sensors 2,which are for example contact sensors attached to the slots. The mediumcontroller provided with the sensors 2, on receiving output from thedoor open detecting means 19, recognizes that a medium entry/exit-enableaction, then checks medium storage information before the mediumentry/exit-enable action occurred and writes the medium storageinformation in the temporary memory 12 (Step 1). The medium controllerrecords status changes in the sensors in the log tracer 16 while thedoor is open. When the door closed detecting means 21 detects that thedoor is closed, the log trace determiner 17 decides from contents of thelog tracer 16 whether or not there is a change in the status of thesensors 2 of the slots (Step 2).

When it has been confirmed that there is no change in the status of thesensors, medium storage information after a medium went out and a mediumcame in is not updated, so that medium storage information before exitor entry of medium is maintained as it is (Step 7). If it could beconfirmed that there is some change in the status of a sensor 2 in Step2, decision is made to which patterns shown below the status transitionsof sensors 2 at the respective slots belong (Step 3). When a decision ismade that the sensor status shifted as ON→OFF, the medium is regarded asremoved, and the associated medium information is erased from mediumstorage information (Step 5). If it is decided that the sensor statusshifted as OFF→ON→OFF, the medium is regarded as stored in the slot buteventually taken out, so that medium storage information is not updated(Step 7).

If it is decided that the sensor status shifted as OFF →ON, the mediumis regarded as stored in the slot, or if it is decided that the sensorstatus shifted as ON→OFF→ON, the medium is regarded as having beenreplaced. Consequently, the medium transfer unit moves to the positionof the corresponding slot and a sensor (different from the one installedin the slot, but not shown) or a bar-code reader installed on the mediumtransfer unit is used to read and recognize new medium information (Step4). Medium storage information, checked at Step 1 and recorded in thetemporary memory 12, has the change-affected portion only updated andbecomes new medium storage information after the medium went out andcame in (Step 6). Steps 2 to 6 are sequentially executed for all slots(sensors 2), and by writing the contents of the temporary memory 12 inthe medium storage information memory 11, the process is completed.

The important point to note is that with the slots other than thosewhose sensors are judged to have shifted as OFF →ON or ON→OFF→ON, it isnot necessary to execute the process at Step 4 of reading mediuminformation from the medium. This reduces the mechanical movement of themedium transfer unit, which results in a notable effect of increasedprocessing speed.

Description will next be made of a second embodiment of the presentinvention with reference to the configuration of the system in FIG. 5and the flowchart in FIG. 2. FIG. 2 is a flowchart of the updatingprocess of medium storage information in a case where a sensor ismounted on each magazine. Referring to FIG. 4, the sensor 5 has aphoto-sensing device installed at the entrance side of the slots of themagazine to detect incoming and outgoing of a medium. More specifically,the sensor 5 comprises a photoemitter 5 a and a photodetector 5 b todetect a medium 3 passing across the optical path of light 6 emittedfrom the photoemitter 5 a. When a medium 3 passed, the sensor managingmeans 14 shown in FIG. 5 recognizes that a medium entry/exit action tookplace. In the case of the second embodiment, there are two kinds ofstatus changes for one sensor: whether a medium entry/exit-enable actionoccurred or not. Therefore, the log tracer 16 in the sensor managingmeans 14 in FIG. 5 may be omitted.

When the medium information controller 18 recognizes that a mediumentry/withdraw-enable action occurred, it checks medium storageinformation before the medium entry/withdraw-enable action (Step 1).Subsequently, a check is made to see if the status of the sensor 5 ofthe slot has changed (Step 2). If it is confirmed that there is nochange in the status of the sensor, medium storage information beforethe medium input/output enable action is not updated as in FIG. 1 (Step8). For the magazine 7 in which a medium blocked the light of theoptical sensor 5 attached to the magazine 7, the status of medium changeis checked for all slots of the magazine by the medium informationreading means 13 through a sensor mounted on the medium transfer unit(not shown) or a bar-code reader (not shown) (Steps 4 and 5).

The whole medium storage information in the magazine may be updated.Alternatively, however, a decision is made for each slot as shown inFIG. 2, and if the decision is that a medium does not exist (Step 4),medium information is erased (Step 7). On the other hand, if thedecision is that there is a medium in the slot (Step 4), a decision ismade whether or not medium information of the slot has changed, and ifthe decision is that the medium information remains the same, it isconcluded that the medium information need not be rewritten as far asthis slot is concerned and this Step is carried out for the next slot(Steps 9 and 10), and if the decision is that the medium information haschanged, the medium information that has been read is written in thetemporary memory 12 so that medium storage information is updated (Step6). After this, if all slots in the magazine have not been checked (Step9), medium information of the next slot is read (Step 10), and adecision is made whether or not a slot is stored in the next slot (Step4). Subsequently, this procedure is repeated until all slots have beenchecked. When all slots in the magazine have been checked (Step 9), theprocess for this magazine is finished. When the process for one magazineis finished and if there is another magazine where there were outgoingand incoming of a medium, the same process is executed on this magazine.

Besides the above-mentioned optical sensor, another method by which tomake the medium controller to decide whether a medium went in and out isby a weight sensor, which detects a change in the weight of themagazine.

If medium information is updated every time a medium goes out of or intothe magazine, accurate and quick updating of medium storage informationcan be achieved. More specifically, when a medium input/output-enableaction occurred, inquiry is made only of the place where a changeoccurred (into all slots of the change-involved magazine) withoutchecking all medium storage places (slots) with a sensor or a bar-codereader mounted on the medium transfer unit. In other words, it is notnecessary to check the slots of the magazine where no change occurred,with a sensor or through bar codes and accordingly, processing speedbecomes faster than in prior art.

Supplementary explanation of the preferred embodiments and applicationsof the present invention will be given in the following.

Description will be made of how the sensors 2 are mounted. FIG. 3 showsan example wherein switch sensors 2 are mounted in all slots and FIG. 4shows an example wherein an optical sensor 5, consisting of a sensorphotoemitter 5 a and a sensor photodetector 5 b, is mounted at themedium entrance of the magazine, both of which can be realized easily.Mounting sensors in individual slots costs a large amount of money, butif an optical sensor is mounted for each magazine as shown in FIG. 4,this arrangement is less expensive. In FIG. 3, the condition that asensor is pressed by a medium placed in the medium storage place isdesignated as ON and the condition that a sensor is not pressed by amedium because there is no medium in the storage place is designated asOFF. In FIG. 4, when light 6 emitted by the photoemitter 5 a is blockedin a given magazine, the medium controller can recognize that a mediumwent in or out of some slot in the magazine.

Next, description will be made of cases where the present invention canbe applied. There is a risk that the medium controller is unable toobtain medium storage information because of some human intervention,for example, in the input or output of a medium to or from mediumstorage for medium managing or in the maintenance work of the mediumcontroller. When there is human intervention, any of the actions occurs,such as opening and closing of the entry/exit door, stopping orsupplying power to the medium controller. The medium controller candetect the occurrence of those events easily by well-known technology.

When there is human intervention in the operation of the mediumcontroller, in other words, when the medium entry/exit door is openedand then closed, or the power to the medium controller is turned offthen on, or system reset, the medium controller recognizes that any ofthose events took place, by using well-known technology. By replacingthe door open detecting means 19 in FIG. 5 by human interventiondetecting means, a reset system action and medium controller poweroff-on action being taken can be considered to be the same as theentry/exit door being opened or closed. Then, when the entry/exit doorwas opened or closed and a reset system action and a medium controllerpower off-on-action was taken, the medium controller calls a mediumstorage information table from the medium storage information memory 11into the temporary memory 12. Subsequently, the log trace determiner ofthe sensor managing means 14 finds a change in the sensor 2 to recognizethat a medium was taken in or out, and updates only the change-relatedportion of medium storage information in the temporary memory 12. Afterhuman intervention, whenever a job is executed by the host computer andconsequently medium storage information is updated, medium storageinformation in the temporary memory 12 is updated. After the job isterminated, medium storage information of the latest version is storedin the medium storage information memory 11.

When the power was switched off and if power supply for the processshown in FIG. 1 is provided as a separate system and can be used, thesame operation as mentioned above can be performed. Even if power supplyis not provided as a separate system, it is possible to grasp just likethe medium status when the power is switched off and on. Namely, dooropen operation is replaced with power off operation and door closeoperation is replaced with power on operation and in FIG. 5 and a doorclose detector 21 is replaced with power on detector, after power isswitched on, medium information before power off operation is put in thesensor status holder and medium information after power on operation isput in the log holder. Then medium information is updated in log tracerdeterminer, and it is easy to determine status changes.

In updating medium information proposed by the present invention,accurate and high-speed updating of medium storage information can beachieved by checking only the place where a change occurred (a slot inthe first embodiment in FIG. 3 or a magazine in the second embodiment inFIG. 4) without having to check all slots with a sensor or a bar-codereader attached to the medium transfer unit when a mediumstorage/exit-enable action took place.

In the process for updating medium storage information according to thepresent invention, as has been described, a medium controller is used,which includes means for recognizing, for example, that the entry/exitdoor is opened or closed and that power supply for the medium controlleris disconnected or supplied, and simple sensors arranged at individualslots and each capable of recognizing whether or not a medium is storedin the slot or sensors arranged at individual magazines and each capableof recognizing whether or not a medium is put in or taken out of theslot. Therefore, when a medium entry/exit-enable action took place, theprocess for updating medium storage information need not check all slotswith a sensor or a bar-code reader arranged on the medium transfer unit,but has only to check the place where a change occurred (a slot or amagazine) to update medium storage information. This configurationallows medium storage information to be updated easily, accurately, andspeedily.

Therefore, time required for updating medium storage information can beshortened sharply, with the result that the present invention offers aneffect to solve the problem that the medium controller is made to waitand cannot execute other processes while the medium transfer unitaccesses all the slots each time a medium comes in or goes out. In amedium controller with a large number of media in storage, in whichtime-consuming medium-storage-information updating job is done by anoperator, the present invention makes it possible to automaticallyupdate medium storage information without intervention by the operatorafter a medium entry/exit-enable action took place, and thus precludesthe problem that medium storage information does not agree with theactual storage status.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications of the illustrative embodiments,as well as other embodiments of the invention, will be apparent topersons skilled in the art upon reference to this description. It is,therefore, contemplated that the appended claims will cover any suchmodifications or embodiments as fall within the true scope of theinvention.

1. A medium controller storing a plurality of media therein, having amedium transfer unit to take a medium in and out of a storage place toread or write information on the medium and to transfer the medium to aplace where reading and writing information is possible, and managinginformation about media in storage, comprising: slots for storing media;sensors, each mounted in each of the slots, for detecting whether or notthere is a medium in said slot; a sensor manager for holding a log ofstatus of said sensors in a period when media are likely to be taken inor out manually and deciding changes in the status of said sensors; anda medium information reader for reading medium information, whichidentifies a medium, from the medium, wherein when it is decided from adecision result by said sensor manager that the medium has beenreplaced, medium information is read by said medium information readerto thereby update medium storage information, or when it is decided thatthe medium has not been replaced, said medium storage information is notupdated.
 2. A medium controller according to claim 1, furthercomprising: a door open detector for detecting that the door is open atthe medium storage place of the medium controller; a door closeddetector for detecting that the door is closed; a first memory forstoring medium management information showing what media are stored inwhich slots; and a second memory for storing medium managementinformation showing what media are stored in which slots at the momentwhen said door close detector detects that said entry/exit door isclosed, wherein said medium storage information is updated by writingsaid medium information, read in by said medium information reader, inthe first and second memories.
 3. A medium controller storing aplurality of media therein, having a medium transfer unit to take amedium in and out of a storage place to read or write information on themedium and to transfer the medium to a place where reading and writinginformation is possible, and managing information about media instorage, comprising: slots for storing media; sensors, each mounted ineach of the slots, for detecting whether or not there is a medium insaid slot; means for deciding changes in status of the sensors in aperiod when media are likely to be taken in or out manually; and meansfor reading medium information, which identifies a medium, from themedium, wherein when it is decided from a decision result by said meansfor deciding changes in the status of the sensors that the medium hasbeen replaced, medium information is read by means for reading mediuminformation to thereby update medium storage information, or when it isdecided that the medium has not been replaced, said medium storageinformation is not updated.
 4. A medium controller according to claim 3,further comprising: means for detecting that the door is open at themedium storage place of said medium controller; means for detecting thatsaid door is closed; first memory means for storing medium managementinformation showing what media are stored in which slots; and secondmemory means for storing medium management information showing whatmedia are stored in which slots at the moment when said door closedetecting means detects that said entry/exit door is closed, whereinsaid medium storage information is updated by writing said mediuminformation, read into by said medium information reading means, intosaid first and second memory means.
 5. A medium controller according toclaim 1, further comprising: a door open detector for detecting that thedoor is open at the medium storage place of the medium controller; adoor closed detector for detecting that the door is closed; a firstmemory for storing medium management information showing what media arestored in which slots; and a second memory for storing medium managementinformation showing what media are stored in which slots at the momentupon said door close detector detecting that said entry/exit door hasclosed, wherein said medium storage information is updated by writingsaid medium information, read in by said medium information reader, inthe first and second memories.
 6. A medium controller according to claim3, further comprising: means for detecting that the door is open at themedium storage place of said medium controller; means for detecting thatsaid door is closed; first memory means for storing medium managementinformation showing what media are stored in which slots; and secondmemory means for storing medium management information showing whatmedia are stored in which slots at the moment upon said door closedetecting means detecting that said entry/exit door has closed, whereinsaid medium storage information is updated by writing said mediuminformation, read into by said medium information reading means, intosaid first and second memory means.
 7. The controller of claim 1,wherein the medium information reader comprises a barcode reader.